Hydrogen Chloride is very soluble in water but it's absorption is complicated by the high heat of solution and the high partial pressure over warm concentrated solutions. In practice, the basic problem in making concentrated solutions is one of efficient heat removal. In this type of absorber, the heat of absorption is removed by evaporation of water and acid in the column. The vapour being condensed is diluted with 'makeup' therefore mostly removed via condenser. Concentration and cooling of the liquid phase is assisted by evaporation of water to maintain the vapour/liquid equilibrium in the lower part of the packed section

The arrangement of the absorber is common to all sizes in the range. The gas is introduced into the column at a point below the packed section and rises counter current to a down comer stream of acid.

'Makeup' water enters above the condenser and in ert gases are vented from the head of the column. The hot concentrated products is passed through an acid cooler before flowing to a storage tank.